Electrical circuit for cold cathode tubes



' Oct. 27, 1936. H. sT. LAURENT, 2,058,738

ELECTRICAL CIRCUIT FOR COLD CATHODE TUBES Original Filed Oct. 23, 1953INVENTOR HERBERT ST. LAURENT TORNEYS Patented Oct. 27, 1936 ELECTRICALCIRCUIT FOR COLD OATHODE TUBES Herbert St. Laurent, Hastings-on-Hudson,N. Y., assignor to Radio Research Laboratories, Inc., New York, N. Y., acorporation of Delaware Application October 23, 1933, Serial No. 694,740Renewed April 20, 1936 4 Claims.

This invention relates to an electrical circuit for use with a coldcathode, or gaseous discharge, device such as those disclosed forexample, in copending applications Serial No. 519,498, filed 5 March 2,1931 andNo. 548,410 filed July 2, 1931 by John A. Heany and Philip M.Haficke. Those applications disclose a tube in which there is anappreciable content of gas and in which an electron discharge occursbetween electrodes which are not heated. As disclosed in thoseapplications these electrodes, which are all within the envelope, maycomprise a cathode, cathanode, control electrode and anode. Theelectrodes may be arranged concentrically in the order named and (1) theinternal electrode may be the cathode while the external electrode isthe anode; or (2) they may be arranged oppositely so that the internalelectrode is the anode and the external electrode is the cathode. A tubearranged in accordance with (1) above is called herein an internalcathode tube, while a tube arranged in accordance with (2) above iscalled an external cathode tube.

The electrodes may also be plain and arranged parallel to one anotheralong a common axis,

as disclosed for example in my copending application Serial No. 605,189,filed April 14, 1932.

This invention has particular reference to tubes in which the externalelectrode is used as the cathode. This type of tube has usually provedto be much more sensitive to weak signals than tubes of the internalcathode type. This is prob ably due to the fact that the larger cathodesurface of the external cathode type of tube generates more electronsand consequently increases the mutual or trans-conductance of the tube.These tubes, however, have presented difiiculties in use due to the factthat they are frequently unstable. When they have been connected in acircuit of a radio receiver, for example, and the circuit adjusted formaximum sensitivity, they tend to oscillate with any change of thetemperature of the gas within the tube, which of course causes a changeof pressure, or when the circuit is tuned to a different frequency. Itis possible to use such a tube with my new circuit in a radio receiveror other electrical circuit in any manner in which an ordinary vacuumtube may be used, and due to the improved characteristics of such 5 atube over vacuum tubes, to obtain much better results.

In the drawing,

Fig. 1 is abroken away View of an. external cathode tube which may beused with the circuit 5 of my invention; and

Fig. 2 shows a circuit diagram of the invention.

In the drawing there is shown a gaseous discharge device I, in whichthere is a cathode 2,

a cathanode 3, a control electrode i, and an anode 5. As previouslystated, this inventionis 5 particularly adapted for use with tubes inwhich the electrodes are arranged concentrically and the cathode 2 isthe external electrode, as shown in Fig. 1. It may, however, be usedwith the other types of arrangement disclosed in the afore- 10 mentionedcopending applications. An antenna 6 is connected to ground through aprimary coil 1. A secondary coil 8 is connected on one side to thecontrol electrode 4, and on the other side through a variable resistance9 to the cathanode 15 3. A variable condenser Ill is connected in serieswith a condenser H across the secondary 8, and may be adjusted to tunethis circuit to a received radio Wave. A battery indicated by plus andminus signs has its positive pole connected to the anode 5 through aresistance 12. The output of the tube is taken off across thisresistance through a condenser IS. The negative pole of the battery isconnected through a resistance I4 to the cathode 2, and through aresistance 15 to the cathanode 3. It will be noted that this pole isalso connected through resistance l5, variable resistance 9 and coil 8to the control electrode 4.

If the resistance 9 is short circuited and the circuit 8|0 tuned to areceived radio wave, there will, as before stated, be a tendency for thecircuit to oscillate. If the variable resistance 9 is adjusted so thatits resistance increases, however, this tendency is eliminated and thetube and circuit operate with highly satisfactory results.

Although I have been unable to form any theory of the operation of thiscircuit which fully satisfies me, it is my belief that the followingexplanation is correct. An incoming signal is im- 40 pressed on thecontrol grid 4, the frequency being selected by coil 8 and condenserIll. The control grid 4 and the cathanode 3 being in the negative glowof the cathode 2, the current from anode 5 tends to shiftt-o theelectrode having the 45 higher potential. With resistor 9 shortcircuited electrodes 3 and 4 have approximately the same D. C. potentialand the anode current is consequently fed back to the input circuit inphase with the impressed oscillations through whichever 5 electrode isat a higher potential due to these impressed oscillations. When theresistance of the Variable resistance 9 is increased, however, thiscauses the electrode 4 to be at a difierent potential than that of theelectrode 3, and new tralizes the tendency to feed back into the controlcircuit. This potential difference need be only slightly larger than thesignal input voltages.

Whatever may be the true explanation of the operation of this circuit,however, the circuit itself operates very satisfactorily as anamplifier, detector, or modulator in a radio circuit.

What is claimed is:

1. A gaseous discharge device of the external cathode type having anenvelope, a cathode, cathanode, control grid, and anode within saidenvelope, an input circuit connected across said control grid andcathanode, an output circuit connected across said anode and cathode andcoupled to said input circuit to produce an inherent tendency toregeneration, and means comprising a variable resistance connected insaid input circuit for preventing regeneration of said circuit.

2. A gaseous discharge device of the external cathode type having anenvelope enclosing the electrodes, an electrical circuit comprising aninput circuit and an output circuit coupled to said input circuit sothat there is an inherent tendency to regenerate, and means forpreventing regeneration in said device and circuits, said meanscomprising a variable resistance in said input circuit.

3. A gaseous discharge device of the external cathode type having anenvelope, a cathode, a cathanode, a control grid, and an anode withinsaid envelope, an input circuit for said device, an output circuit forsaid device coupled to said input circuit to produce an inherenttendency to regenerate, and means connected in said input circuit forcontrolling regeneration in said device and circuits.

4. A gaseous discharge device comprising a cathode, cathanode, controlgrid and anode, a source of potential, a resistance connected betweenthe positive pole of said source and said anode, an output circuitconnected across said resistance, a second resistance connected betweenthe negative pole of said source and said cathode, a third resistanceconnected between the negative terminal of said source and saidcathanode, and a variable fourth resistance connected between said thirdresistance and said control grid.

HERBERT Sr. LAURENT.

